When entering a burning building, firefighters wear breathing apparatus consisting of an air tank, regulator, face mask and pressure gage. Typically, firefighters work in dense smoke, where the visibility may be only a few inches.
Firefighters carry a personal alert safety system (PASS) device, which activates an audible alarm, if they stop moving. The PASS device has a “Pre-Alert” stage, which allows the firefighter a pre-specified number of seconds to move or to shake the PASS device, before the alarm is activated. In addition to the PASS device, firefighters need to know certain information about their constantly changing situation in order to safely and efficiently perform their work.
At minimum, firefighters need to know at all times, how much air is remaining in their tank. The pressure of the air tank will only tell part of the story. Two firefighters with identical pressure gage readings may each have a different number of minutes of air time remaining, depending on their respective rates of air consumption. The rate of air consumption varies from firefighter to firefighter according to size, physical conditioning, and metabolic rate. The rate of air consumption also can change from minute to minute for an individual firefighter depending on the intensity of the physical work being performed, stress, and other factors. Therefore, the firefighter needs to know both the air pressure and its equivalent in number, of minutes remaining, at any given time.
For safety reasons, the firefighter also needs to know the ambient temperature, its time-dependent effect on his or her cumulative heat stress level, and whether flashover conditions are impending. Before opening a door inside a burning building, the firefighter needs to know whether there is a raging fire on the other side. During so-called “mop-up” operations after the fire has been extinguished, firefighters typically have to use axes to inspect inside walls, to ensure that no hidden fires exist.
Firefighters wear thick gloves, carry axes and water hoses, and need their hands free to be able to perform their work. Gages that attach to the air hose and hang from the firefighter's side are inconvenient to continuously pick-up and, in dense smoke, are almost impossible to read. When brought up to the face mask, the gage is too close for the firefighter's eyes to focus. For this reason, an elementary display system has recently been invented, consisting of a series of Light Emitting Diodes (LEDs) mounted inside the face mask. The drawback to this approach is that the LEDs provide much less information than gages provide.
A helmet-mounted display system such as those used by military jet fighter pilots, which projects data onto the visor of the helmet, would offer firefighters a possible solution. However, the cost of a single helmet could absorb an annual budget. The cost to equip all firefighters worldwide would be staggering.
Another occupational group working with impaired visibility are welders. When welding certain types of material, such as stainless steel or aluminum, certain amperage settings for the welds may be specified in the manufacturing drawings, and it is necessary to the welder from time to time to check the amperage gage. In many cases the welder has to work several meters away from the welding machine, and he has to flip up his helmet and walk back to read the gage. If the welder is working on a ladder or a scaffold, he has to climb down or ask someone else to read the amperage.
Remote controls for setting the amperage are available, and to save time welders sometimes try to set the amperage based on experience. If the amperage is set incorrectly with this method, the result can be a weld that is out of the specification or a rejected part.
Also soldiers suffer from impaired visibility when chemical warfare agents (CWA) are present and they have to wear gas masks and protective clothing. Sometimes soldiers have to work in even more impaired visibility conditions, for example after a bombardment the battlefield is covered with smoke.
Soldiers carry CWA detection instruments, which indicate the presence of any chemical warfare agent. When the CWA detection instrument detects the presence of CWA, it activates an audible alarm, and soldiers put on their gas masks and protective clothing. The CWA detection instrument continues to monitor the level of present CWA, and informs the soldiers when it is safe to take of the gas mask.
The CWA detection instrument also continuously measures the concentration of chemical warfare agents in the surrounding. To be all the time aware of the current concentration, soldiers need to look at the instrument frequently. Current instruments are handheld and soldiers need pick them up to read them, same time forcing him to release grip from his tools or weapon.
Displays of these current handheld instruments are small and they are not protected from mud and dirt. Also dense smoke can impair the readability of the instrument. To improve the readability of these current CWA detection instruments their displays are often illuminated. This in turn can reveal the soldier to the enemy. One detection instrument is also needed for each soldier, which adds weight to the soldier's gear and increases costs.
The incident commander (IC) is in charge of all firefighters at the scene of the fire. Each firefighter gives the IC a personal accountability tag (PAT) upon arrival at the scene. The IC keeps track of the firefighters by the use of a unit identification pad (UIP) and a large marker board. The drawback is that once the firefighters are inside the fire, the IC has no method of knowing how much air each firefighter has left, what temperature the firefighters are operating in, what is their heat stress level or PASS device status.
The commanding officer (CO) of a certain part of the battlefield is tracking the overall CWA concentration of that area. Soldiers report their instrument readings to the CO either using a radio or a courier. The drawback is that the CO can not keep track of the CWA concentration or the dosage of an individual soldier in real time.
Firefighters, welders and soldiers are just examples for possible users of digital situation indicator of the invention. This kind of indicators can be utilized in many fields where personal monitoring and alarming are essential.